1. Field of the Invention
In general, the present invention relates to counterbalance systems for windows that prevent open window sashes from moving under the force of their own weight. More particularly, the present invention system relates to the structure of both the brake shoe and window track stops that help inhibit the unintentional movement, known in the industry as drift, of a window sash during use.
2. Description of the Prior Art
There are many types and styles of windows. One of the most common types of window is the double-hung window. Double-hung windows are the window of choice for most home construction applications. A double-hung window consists of an upper window sash and a lower window sash. Either the upper window sash or the lower window sash can be selectively opened and closed by a person sliding the sash up and down within the window frame.
A popular variation of the double-hung window is the tilt-in double-hung window. Tilt-in double-hung windows have sashes that can be selectively moved up and down. Additionally, the sashes can be selectively tilted into the home so that the exterior of the sashes can be cleaned from within the home.
The sash of a double-hung window can be very heavy. The weight of the window sash depends upon both the materials used to make the window sash and the size of the window sash. Since the sashes of a double-hung window are free to move up and down within the frame of a window, some counterbalancing system must be used to prevent the window sashes from constantly moving to the bottom of the window frame under the force of their own weight.
Modern tilt-in double-hung windows are primarily manufactured in one of two ways. There are vinyl frame windows and wooden frame windows. In the window manufacturing industry, different types of counterbalance systems are traditionally used for vinyl frame windows than for wooden frame windows. The present invention is mainly concerned with the structure of vinyl frame windows. As such, the prior art concerning vinyl frame windows is herein addressed.
Vinyl frame, tilt-in, double-hung windows are typically manufactured with guide tracks along the inside of the window frame. Brake shoe assemblies, commonly known as “shoes” in the window industry, are placed in the guide tracks and ride up and down within the guide tracks. Each sash of the window has two tilt pins or tilt posts that extend into the shoes and cause the shoes to ride up and down in the guide tracks as the window sashes are opened or closed.
The shoes contain a brake mechanism that is activated by the tilt post of the window sash when the window sash is tilted inwardly away from the window frame. The shoe therefore locks the tilt post in place and prevents the base of the sash from moving up or down in the window frame once the sash is tilted open. Furthermore, the brake shoes are attached to coil springs inside the guide tracks of the window assembly. Coil springs are constant force springs, made from a coiled length of metal ribbon. The coil springs supply the counterbalance force needed to suspend the weight of the window sash.
Small tilt-in windows have small, relatively light window sashes. Such small sashes may only require a single coil spring on either side of the window sash to generate the required counterbalance forces. However, due to the space restrictions present in modern tilt-in window assemblies, larger springs cannot be used for heavier window sashes. Rather, multiple small coil springs are ganged together to provide the needed counterbalance force. A large tilt-in window sash may have up to eight coil springs to provide the needed counterbalance force.
The coil springs used to counterbalance the weight of a window sash typically only approximate the weight of the window sash. Often, the upward force of the coil springs is slightly less than the downward force of gravity. A window manufacturer, therefore, relies on friction to retain the window in an open position. However, as windows wear, surfaces become smooth and friction can be significantly reduced. Accordingly, when a window sash is fully open, it may begin to drift closed without being touched. Furthermore, when an upper window sash is being opened, it creates friction against the lower window sash that it passes. If the lower window sash is opened, then the movement can cause the open upper window sash to drift closed.
A need therefore exists for a system and method that can prevent a window sash from drifting under the force of its own weight as friction forces vary over time. This need is met by the present invention as described and claimed below.